1. Field of the Invention
This invention relates to a solid catalyst component for .alpha.-olefin polymerization and a process for producing the same.
More particularly the present invention relates to a novel supported type solid catalyst component for supported type Ziegler-Natta catalysts, obtained by dissolving an anhydrous magnesium dihalide, a titanic acid ester and an alcohol in an inert hydrocarbon solvent, mixing and reacting the resulting solution with a silicon halide, an organic acid ester and an aluminum halide and further reacting the resulting solid product (I) with a titanium halide and/or a vanadium halide, and a process for producing the same.
.alpha.-Olefin polymers referred to in the present invention mean homopolymers of .alpha.-olefins having 3 or more carbon atoms and copolymers of .alpha.-olefins having 3 or more carbon atoms with .alpha.-olefins different from the above and having 2 or more carbon atoms, the proportion of the former .alpha.-olefins in the copolymers being 50% by weight or more.
2. Description of the Prior Art
Heretofore, in order to improve Ziegler-Natta catalysts, those which have a high polymerization activity and also can afford a highly stereospecific polymer have been energetically pursued. In recent years, however, it has come to be required for the catalysts that in addition to the above propoerties, the catalysts are to be further provided with a property due to which the polymer can also have a good particulate form. In the present invention, such a good particulate form of polymer particles refers to (1) a fact that the form of polymer particles is spherical or nearly spherical, (2) a fact that the particle diameters of polymer particles are within a definite range and the particle diameter distribution of polymer particles is extremely narrow and (3) a fact that the proportion of polymer particles having an extremely small particle diameter i.e. the so-called finely divided powder present in the polymer particles is extremely small.
Such a good particulate form of polymer particles brings about a great effectiveness. For example, particularly in the gas phase polymerization process which is carried out without any solvent in principle and hence commercially very economical, the resulting polymer has a good fluidity to make possible a long term stabilized operation of polymerization apparatus. Further, in the .alpha.-olefin polymerization, practically no adhesion of polymer to the inner wall of polymerization vessel or stirrer occurs, to ease polymer withdrawal from the polymerization vessel and make it possible to carry out polymer production in the same apparatus, for a long time, continuously and in stabilized manner.
Further, such a good particulate form of polymer particles brings about the following advantages a.about.g with respect of production in the steps subsequent to the polymerization step:
a. It is easy to separate polymer from solvent in the slurry polymerization process.
b. It is easy to transport or recover polymer.
c. Feed of polymer to granulator and operations at the time of processing and molding are easy.
d. It is possible to inhibit dust explosion due to the presence of finely divided powder, and since the amount of finely divided powder is small and handling of polymer particles is simplified, productivity is improved.
e. In the case of copolymerization process, it is possible to inhibit inferiority in the form of polymer particles and reduction in the bulk density due to copolymerization. Namely, copolymer production becomes easy.
f. It is possible to omit the expensive polymer granulation step in the case of certain use applications or transportation manners of polymer.
g. All the above advantages a.about.f contribute directly or indirectly to energy saving or resources saving and further make it possible to improve the quality of polymer in respect of product homogenity; as a result, it is possible to correspond to new market needs concerning the quality.
Now, in the olefin polymerization by means of Ziegler-Natta catalysts, it has been known that there is a close relationship between the particulate form of the resulting polymer and the particulate form of the solid catalyst used. Namely, it has been observed that the particulate form of the solid catalyst is reflected on that of the polymer. Thus, for improving the particulate form of the polymer, it is necessary to improve the particulate form of the solid catalyst to be used, and also it is necessary that the catalyst retain a strength to such an extent that it is not ground when used, i.e. during the polymer production process.
As for supported type catalysts for .alpha.-olefin polymerization, it has so far been known that an anhydrous magnesium halide, an organic acid ester and a titanium halide are reacted by co-milling to give a solid catalyst affording a high polymerization activity and a highly stereoregular polymer (Japanese patent application laid-open No. Sho 50-1269590/1975). However, even if .alpha.-olefins are polymerized using such a solid catalyst, it is impossible to obtain .alpha.-olefin polymers having a good particulate form, since the particulate form of the solid catalyst used is irregular and the particle size was not specified.
Now, anhydrous magnesium halides are per se insoluble in inert hydrocarbon solvents. However, it has been known that if anhydrous magnesium halides are reacted with orthotitanic acid esters and/or alcohols, anhydrous magnesium halides are soluble in inert hydrocarbon solvents. Utilizing such a solubilizing reaction, for example Japanese patent application laid-open No. Sho 54-40293/ 1979 proposes a process wherein anhydrous magnesium chloride, butyl orthotitanate and n-butanol are heated together with heptane and uniformly dissolved and SiCl.sub.4 is added to the resulting solution to deposit solids, followed by reacting the solids with a complex of TiCl.sub.4 and ethyl benzoate obtained by dissolving these in n-butyl chloride to obtain a solid catalyst component. The above laid-open application also proposes as an alternative process, a process wherein anhydrous magnesium chloride, butyl orthotitanate and ethyl benzoate are heated in n-butyl chloride, followed by first reacting SiCl.sub.4 to deposit solids and then reacting TiCl.sub.4 with the solids to obtain a solid catalyst component. However, judging from this alternative process, alcohols are not indispensable compounds for dissolving anhydrous magnesium chloride in an inert hydrocarbon and affording sufficient catalyst performances. Thus, even if propylene is polymerized using he catalysts obtained by these processes, the polymerization activity of the catalysts is not high enough to make it possible to omit removal of catalyst residue contained in the resulting polypropylene. Further, the stereoregularity of the polymer obtained by polymerizing .alpha.-olefins by the use of this catalyst is insufficient, and moreover the above laid-open patent application has no description as to the particulate form of the polypropylene obtained according to the process of the application.
Next, Japanese patent application laid-open No. Sho 58-32604/1983 proposes a process wherein anhydrous magnesium chloride, butyl orthotitanate and ethyl toluylate are heated in heptane to prepare a uniform solution, which is then reacted with SiCl.sub.4 to deposit solids, which are then washed with an inert solvent and thereafter reacted with TiCl.sub.4 to obtain a solid catalyst. However, the performance of the catalyst obtained according to this process is still insufficient in the yield or stereoregularity of the resulting polymer. Further the above application has no description as to the particulate form of the polymer except for a description that the particle diameter distribution of the resulting polymer is narrow.
According to Japanese patent application laid-open Nos. Sho 56-811/1981 and Sho 56-11908/1981, anhydrous magnesium chloride is reacted with an alcohol and the resulting material is dissolved in a hydrocarbon solvent, followed by adding to the solution a titanium halide or a silicon halide for re-solidification to obtain a solid catalyst. However, Examples of the above applications have no concrete description as to the particulate form of polymer.
According to Japanese patent application laid-open No. Sho 56-136805/1981, anhydrous magnesium chloride is reacted with an alcohol and the resulting material is dissolved in a hydrocarbon solvent, followed by reacting a titanium halide therewith for solidification to obtain a solid catalyst. However, it is an indispensable requirement for the process to have a liquid hydrocarbon contained in the solid catalyst in an amount of 10 to 25% by weight to thereby control the particulate form of the polymer.
According to Japanese patent application laid-open No. Sho 57-74307/1982, it has been attempted to improve the particulate form of polymer by pretreating the solid product with an organoaluminum compound, in addition to the process of the above application No. Sho 56-1136805. However, in any of the processes disclosed in Japanese patent application laid-open Nos. Sho 56-811 to Sho 57-74307, orthotitanic acid esters and/or polytitanic acid esters are not indispensable compounds for dissolving anhydrous magnesium chloride in an inert hydrocarbon and affording sufficient catalyst performances.
Thus, any of the solid catalysts obtained according to the foregoing processes do not fully satisfy all of the polymerization activity, the stereoregularity and the particulate form of polymer.
As described above, according to the prior art, it has been possible to solubilize anhydrous magnesium dihalides in inert hydrocarbon solvents by using the dihalides together with titanic acid esters or alcohols. However, their re-solidification has been difficult. As a result, it has also been difficult to control the particulate form of the solid catalysts, and ultimately no polymer having a good particulate form has been obtained.
In order to solve the above problems of the prior art, the present inventors have made extensive research, noting the process of solubilizing anhydrous magnesium dihalides in an inert hydrocarbon solvent, followed by re-solidification. As a result, by using a solid product obtained by reacting anhydrous magnesium dihalides with a titanic acid ester and an alcohol at the same time to thereby easily solubilize the dihalides in an inert hydrocarbon solvent, and also reacting the resulting solution with an organic acid ester, an aluminum halide and a silicon halide, it has become possible to enhance the stereoregularity of olefin polymers obtained by using a finally obtained catalyst; to control the particulate form of the carrier for solid catalyst obtained by using a relatively small amount of the silicon halide; and to ultimately obtain a solid catalyst having a good particulate form and being resistant to grinding.
As apparent from the foregoing, the object of the present invention is to provide a solid catalyst component which has a high polymerization activity to such an extent that it is unnecessary to remove the catalyst remaining in polymer, and also which can afford a highly stereoregular polymer having a good particulate form, and a process for producing the same as well as a process for utilizing the same.